The general objective is to determine the response of cells in the pars distalis and pars tuberalis of the pituitary gland to natural and synthetic estrogens and progestins, including oral contraceptive agents. The primary technical procedure is immunocytochemistry used with both light and electron microscopes. Much of the work is on the monkey but some deals with man and the rat. Emphasis will be placed on the cells secreting prolactin, FSH, and LH, and on the hormones that regulate these cells. An important aspect of the project is an attempt to differentiate the cellular origins of the glycoprotein hormones: TSH, LH, and FSH. With the monkey, cytological changes in the pituitary gland will be correlated with the changing concentrations of prolactin, LH, and FSH in the blood serum as determined by radioimmunoassay during the menstrual cycle.